A huge amount of rapeseeds that are used as oil seeds is mainly imported from abroad.
A rapeseed contains approximately 40-45 wt % of oil, which is the highest ratio among those of oil seeds including soybean, sesame and the like. For that reason, mechanical expression of the rapeseed can be easily carried out, and the rapeseed is a very useful material for vegetable food oil and fat.
A rapeseed oil is usually produced by first flaking the rapeseed, then subjecting the flaked rapeseed to a heat treatment, and finally expressing it by means of an expressing machine named an "expeller" so as to obtain about 1/2-3/4 of the total oil contained in the rapeseed. The oil remaining in an expression cake, i.e., the cake obtained in the expression process, is then extracted with n-hexane.
The oil that is obtained by the expression process (referred to as "expression oil" hereinafter) and the oil that is obtained by the extraction process (referred to as "extraction oil" hereinafter) are combined and purified to give the rapeseed oil.
On the other hand, after being separated from the solvent, an extraction cake that is obtained in the extraction process is utilized mainly as fertilizer or feed. However, as these by-products other than oil is sold at a very low price, it has been desired to more effectively utilize the above by-products.
For example, it has been tried to increase a protein content by removing a hull from the rapeseed, or to increase a value of the extraction cake as feed by removing bitterness components such as tannin from it with water or an organic solvent.
Like the other oil seeds, the rapeseed consists of a cotyledon, a hull and a germ. The germs of the oil seeds other than the rapeseed, such as those of soybean, wheat, rice, corn and the like have already been actually utilized.
On the other hand, since the germ of a relatively small oil seed such as the rapeseed (ca. 1.9 mm in diameter) is very small (ca. 1.5 mm in length and ca. 0.5 mm in diameter), when compared with that of corn (ca.8 mm in length, ca.3 mm in width, and ca.2 mm in thickness), an attention has been hardly made to the rapeseed germ and no try has been made to separate and utilize a fraction of the rapeseed that has a high germ content.
The investigation of the present inventors has revealed that the ratio of the germ content in the rapeseed is approximately 12 wt %, which is much higher than that of soybean (ca.2-3 wt %).
It is therefore expected that an efficient separation and recovery of the rapeseed germ in an industrial scale could expand its utility.
For the purpose of efficiently separating and utilizing the rapeseed germ, the present inventors have studied and found that not only the hull but also the germ can be peeled off from the cotyledon during the crushing process of the gains of the rapeseed under compact stress so as to efficiently separate a fraction containing its germ as a main component. It is also revealed that the thus separated fraction has such a higher germ content as about 95 wt % at maximum than that of the soybean (75 wt % at maximum).